The present invention generally relates to communication systems, and in particular to a system and method for improving noise and interference immunity in a wireless communication system.
Recently a standard for short range wireless communication has evolved known as the Bluetooth standard (see www.bluetooth.com). Bluetooth is a Radio Frequency (RF) specification for short range, point to multi-point voice and data transfers. Bluetooth can transmit through solid, non-metal objects. It has a nominal link range from 10 centimeters to 10 meters, but can be extended to 100 meters by increasing the transmit power. It is based on short-range radio links and facilitates ad hoc connections for stationary and mobile communication environments. The Bluetooth standard is a low-cost short range wireless communication standard that typically operates in the 2,400-2,483.5 MHz industrial, scientific and medical (ISM) band. The ISM band is available worldwide and allows unlicensed operation of spread spectrum systems. The Bluetooth standard is often employed for short-distance connections and can be employed to replace cables used today that, for example, connect laptops to cellular telephones, printers, desktops, fax machined, joysticks and many other digital device that can be part of the Bluetooth system. Bluetooth can also provide a bridge to existing data networks. Bluetooth is specifically designed to provide low-cost, robust, efficient, high capacity, ad hoc voice and data networking.
Bluetooth technology has been designed to operate in noisy radio frequency environments and uses a fast acknowledgment and frequency hopping scheme to make a robust communications link. Bluetooth radio modules attempt to avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet as compared to other systems operating at the same frequency band. The implementations of faster hops and shorter packets limit impact of microwave and other sources of interference. Bluetooth uses forward error correction to limit impact of random noise on longer distance link.
In Bluetooth Synchronous Connection Oriented (SCO) links there is no provision for re-sending lost data; and each time a receiver hops to a blocked channel, up to 3.75 milliseconds of sequential audio may be unrecoverable. The lost packets due to fixed interferers are compounded with lost packets from FHSS (Frequency Hopped Spread Spectrum) interference from other FCC (Federal Communications Commission) devices operating in the vicinity to produce noticeably degraded audio for the user. For Bluetooth Asynchronous Connection-Less (ACL) links, different levels of error correction and detection can be put in place to protect against lost or bad data. However, in any case, the error correction or detection often results in reduced bit rate. Other standards in the ISM band also have similar problems associated with channels with strong interference or noisy fixed interferers.